1. Field of the Invention
The embodiments discussed herein relate to a method for multiple registration of a multimodal communication terminal via at least one access network in an IMS-based service communication system of a mobile and/or convergent communication system, where the multimodal communication terminal is registered for at least one communication service via a first access network in at least one service control unit of the IMS-based service communication system.
2. Description of the Related Art
Existing mobile communication systems of the second generation, called “Global System for Mobile Communications” (GSM) mobile communication systems, communication services such as, for example, GPRS (“General Packet Radio Services”) which are based on packet-oriented data transmission, are already available. By this mechanism an improved utilization of the available transmission resources is possible in the associated mobile communication system.
In particular for mobile communication systems of the third generation, i.e. mobile communication systems based on the “Universal Mobile Telecommunication System” (UMTS) transmission technology, special communication systems or, more specifically, service communication systems such as, for example, the “Internet Protocol Multimedia Subsystem” (IMS) communication system are provided for extending the existing GPRS architecture and providing additional multimedia communication services.
Moreover, mobile communication devices are increasingly embodied as multimodal, i.e. they support the most diverse mobile transmission technologies or access technologies. For example, a “Wireless Local Area Network” (WLAN) can be provided as a supplementary access network alongside a UMTS- or GSM-based mobile communication system.
A distinction needs to be drawn between mobile access networks of the kind and communication systems based on the Internet Protocol (IP) which enable IP-based communication services of a network operator to be used. Usually IP-based communication systems of the kind are geared to the mobile transmission technology that is present in each case. For example, the mobile communication systems based on the GSM and UMTS transmission technologies share a common access network based on the GPRS transmission technology, whereas a separate independent access network is required for a WLAN communication network. If a mobile communication terminal now changes the mobile transmission technology or, as the case may be, access technology used for transmitting the data, from WLAN to GSM/UMTS for example, this change additionally necessitates a change of the associated IP-based communication system as well.
Service users connected to the IMS-based communication system are provided with communication or multimedia services via an access network of this kind. At this juncture, voice services, data services, audio services, video services, information services and program communication services may be cited as examples of communication or multimedia services.
A “Session Initiation Protocol” (SIP) signaling protocol is provided within an IMS-based communication system of the kind for the purpose of setting up communication connections. Communication subscribers within the IMS-based communication system are identified via identifiers that remain stable for a long time, called SIP “Uniform Resource Identifiers” (URI), which are structured similarly to a traditional email address.
The IMS-based communication system or service communication system specified by 3GPP can be used independently of the access network, i.e. in addition to the GPRS technology of second- and third-generation mobile communication systems also for WLAN, WiMAX (“Worldwide Interoperability for Microwave Access”) and DSL (“Digital Subscriber Line”). The IP address required for accessing an access network is usually assigned to the multimodal communication terminal by the access network and consequently is linked to this access network. In this context, the term “access network” is used in a very broad sense and includes a gateway network node, e.g. in the case of a WAN access network the “Packet Data Gateway” (PDGW) network node defined in the 3GPP TS 23.234 standard.
The SIP signaling protocol (IETF RFC 3261) provided within the IMS-based communication system requires every mobile communication terminal to register on the IMS-based communication system (3GPP TS 23.228/24.229). In order to implement the SIP signaling protocol, special server units are provided which provide connection and service control functions, referred to as “Call State Control Functions” (CSCF).
An IMS-based communication system of the kind includes, for example, a “Serving Call Session Control Function” (S-CSCF) unit, an “Interrogation Call Session Control Function” (I-CSCF) unit and a “Proxy Call Session Control Function” (P-CSCF) unit which handle different signaling tasks. For example, the SCSCF unit is responsible for registering a mobile communication terminal in the IMS-based communication system, the unit serving according to RFC 3261 to establish a link between the address information at SIP level (SIP-URI) and the address information at IP level (IP address) in order to be able to forward an incoming SIP session with a SIP-URI correctly to the right IP address. In the IMS architecture the authentication is also linked to the registration, which means that the authentication is also a requirement for an outgoing SIP session.
It is provided in particular in 3GPP TS 24.229, paragraph 5.4.1.2.1 that a new registration of a mobile communication terminal under the same SIP-URI (in IMS: “Public User Identity”) and the same user name (in IMS: “Private User Identity”) replaces an already existing registration. By this means it is ensured that in the case of a new allocation of an IP address to a mobile communication terminal as a result of a malfunction affecting the radio connection the old IP address has meanwhile become invalid. Address conflicts can be effectively avoided in this way.
If the user of a multimodal mobile communication terminal changes the access network, it is necessary to allow multimodal mobile communication terminals to register at least temporarily for a plurality of access networks in an IMS-based communication system. In order to ensure a user-friendly change, at least two access networks should be available simultaneously at least for a predetermined transition period.
Although it is possible, in deliberate circumvention of the 3GPP specifications, to force a parallel registration of a multimodal mobile communication terminal by performing a second registration via the S-CSCF unit without deleting the first registration, this can, however, result in undesirable disruptive effects, such as, for example, communication connections being able to continue to be sent erroneously to IP addresses that have become invalid within the IMS-based communication system.
Furthermore it is also possible to use a cross-network “Public User Identity” (SIP-URI), though with different “Private User Identities” (user names). A method of the kind was originally developed for access via physically separate communication terminals. A disadvantage in this case, however, is that a plurality of different “Private User Identities” have to be assigned to the smartcard (ISIM or IMS “SIM card”) contained in the mobile communication terminal, thereby considerably reducing the ease of use of the mobile communication terminal.